Conventional gas engines include a gas engine described in JP 2013-92082 A (Patent Document 1). This gas engine is capable of a stoichiometric operation in which an air-fuel mixture is combusted at a value near a theoretical air fuel ratio with a higher rate of a fuel gas. The gas engine enables the stoichiometric operation so as to facilitate generation of a higher torque so that a high output is easily achieved.
On the other hand, it is conventionally known that a so-called knocking tends to occur in a high torque region of a gas engine. Therefore, it is known that a gas engine performing the stoichiometric operation is disposed with a knock detecting means detecting a sign of knocking. If the knock detecting means detects a sign of knocking, the knocking is avoided by retarding an ignition timing etc. In this way, while the high output can easily be achieved, the knocking is avoided to prevent abnormal combustion for protection against a piston damage etc.
However, the conventional gas engine avoids a knocking on the premise of the detection of a sign of the knocking and cannot avoid the sign of the knocking itself. This leads to a problem that the knocking occurring subsequently to a sign of the knocking cannot properly be avoided.